As a survey of the different roles that modular forms and q-series play in number theory, this monograph describes recent developments in congruences for partitions, basic hypergeometric functions, Gaussian hypergeometric functions, Weierstrass points on modular curves, traces of singular moduli, class numbers of quadratic fields, L-values, and elliptic curves. The opening chapters review basic facts about integer weight modular forms and half-integral weight modular forms. Annotation ©2004 Book News, Inc., Portland, OR (booknews.com)